This invention relates to apparatus for inserting a core member into an open-ended casing, particularly in situations where a close fit or tolerance is desired between the casing and the core member. The apparatus is particularly useful in the manufacturing of electrochemical cells where a coiled electrode assembly must be inserted into a cell casing.
In the assembling of electrochemical cells, particularly sealed cells contained or housed in an electrolyte-impervious casing, it is the usual practice first to make up an electrode assembly and then place this electrode assembly in the cell casing. The external terminals for the cell are provided either prior to or after the electrode assembly is placed into the casing.
A typical electrode assembly is comprised of at least one positive electrode plate and at least one negative electrode plate spaced-apart by intermediate separator layers which contain an absorbed electrolyte. Except for high-capacity battery cells, the electrode assembly usually takes the form of a cylindrical unit comprised of spirally wound positive and negative electrode plates, together with the interleaved separator layer. This coiled electrode assembly is inserted into the casing, terminal connections provided between the electrode plates and the external cell terminals, and the casing sealed to form the finished product or subassembly.
With certain types of cells, e.g., nickel-cadmium cells, the electrode assembly can be inserted into the casing without excessive difficulty owing to the stability of the coiled electrode assembly once it is formed. That is, the nickel-electrode plates, once wound, have a substantial degree of structural integrity, and the separator material used with these cells is also strong and not easily damaged.
In the case of other types of cells, however, such as small sealed lead-acid cells, the lead electrodes are rather soft, and the separator material often is a very fragile fibrous substance. For example, separators cut from a fibrous glass mat are vulnerable to damage upon contact with a hard irregular surface. Should such damage occur as the electrode assembly is being placed into the cell casing, electrical shorting or other operational performance anomalies can result.
A second and related problem in assembling lead-acid cells using soft separator material is the difficulty of achieving a sufficiently tight fit of the electrode assembly inside the casing so as to preclude rattling and/or vibration during use. It is desirable, from the point of view of structural integrity of the cell, to maintain the closest practicable tolerance between core and casing to reduce, or even eliminate, unwanted movement and ultimate loosening and separation of the coiled electrodes and intermediate layers inside the finished cell. In the past, however, it was difficult to achieve solutions to both of these problems. This is because the casings have been generally oversized for two reasons: first, in order to avoid inadvertent damage to the electrode assembly during its insertion into the casing and, second, in order to accommodate tolerance variations in the diameter of the electrode coil. The use of oversized casings is generally incompatible with the achievement of the desired close fit between the electrode coil and casing.
Among the objects of the present invention are to meet and solve the foregoing difficulties in the assembly of electrochemical cells, and to provide improved apparatus which may be used to insert a core member into a casing under varying conditions of tolerance.